It is possible that the influenza strains selected for inclusion in the current influenza vaccines are imperfectly matched antigenically with the viruses causing infection in humans. We have shown that the cultivation of influenza viruses in embryonated chicken eggs (eggs) select subpopulations which are antigenically distinct from virus cultivated from the same source in Madin-Darby canine kidney cells (MDCK). These antigenic differences were detected with monoclonal and polyclonal antibodies to the hemagglutinin molecule. Since antigenic characterization of influenza virus strains for epidemiological purposes and the preparation of influenza vaccines conventionally rely on the cultivation of virus in eggs, our findings may have important practical implications on vaccine design and efficacy. To this end our specific aims are: (1) to determine the influence of host cells on the selection of influenza A and B viruses during primary isolation and (2) to establish the molecular changes in the genes of influenza viruses grown in different host cell cultures. Influenza A viruses of the H1N1, H3N2 and an avian subtype and current influenza B strains will be isolated in eggs and in MDCK cells. The viruses will be characterized antigenically with monoclonal antibodies to the major gene products to determine whether antigenically distinguishable influenza viruses are isolated in different host cells. The homogeneity of the virus in primary culture from the patient will be analyzed to establish whether subpopulations are present. Analysis with polyclonal antisera in neutralization assays and in cross-protection in a ferret model system will establish the extent of cross-protection induced between these antigenically distinguishable viruses. The antigenic stability of the viruses and the optimal host tissues for growth will be established. Under the second specific aim, the antigenic changes will be correlated with sequence changes in the hemagglutinin molecular from different host tissues. The role of the other genes of influenza virus will be analyzed with monoclonal antibodies, by hybridization and by nucleotide mapping to establish which gene constellations are involved in antigenic variation of influenza viruses from different host cell systems. The proposed studies are vitally important in the selection of the most appropriate influenza viruses for use in epidemiological studies and vaccine production.